The present invention relates to a method and apparatus for coating a surface of a substrate such as a semiconductor wafer or an LCD (liquid crystal display) substrate with a desired resist pattern and developing the coated resist pattern.
In photolithography, used is a resist processing system in which a semiconductor wafer is successively coated with a resist solution, followed by developing the coated resist. In a resist coating-developing system disclosed in, for example, U.S. Pat. No. 5,664,254 or Japanese Patent Publication (Kokoku) No. 2-30194, a large number of process units are arranged around a wafer transfer path, and wafers are transferred along the transfer path by a main arm mechanism into each of these process units so as to be processed successively. Since the resist coating-developing system of this type is used in combination with a light exposure unit, wafers are frequently transferred into and out of these coating-developing system and light exposure system.
In recent years, the required line width of a resist pattern is in a deep sub-micron region, making it absolutely necessary to control severely various parameters such as the amount of exposure to light and developing time. In many cases, the parameters for such a line width control are controlled by actually measuring the line width of the resist pattern for sample wafers optionally extracted by an operator. Where the actually measured line width fails to fall within an allowable range of a target value, the operator gives command signals to a host computer for changing various parameters for the line width control.
However, the conventional parameter control system, which depends on the operator's skill, is incapable of constantly improving the line width accuracy. Also, in many cases, the line width of a resist pattern is controlled by correcting the amount of light exposure in the exposure device. However, the required line width of a resist pattern tends to become finer and finer in recent years, with the result that the line width control system noted above is incapable of controlling the line width with a high precision in some cases. Further, a feed back system is employed in the conventional line width control for a resist pattern. In other words, the wafers which are not transferred into the feed back control system are regarded as defective, leading to a low yield. The resultant loss of wafers markedly increases the manufacturing cost of a semiconductor device because the wafers are sized bigger and bigger nowadays. Naturally, it is of high importance to improve the yield of wafers in the process step with resist.